Ensign Wasps Don't Sting People but Will Kill Cockroaches
Ensign Wasps Are Harmless
The Ensign Wasp (Evonia appendigaster) looks a bit like a black spider with wings. Many people, upon seeing one, might assume that it will sting, but in fact it is totally harmless.
The Ensign Wasp is actually a beneficial insect because it is a parasite of cockroaches and hunts for their egg-cases, which are known as oothecae. The female wasps lay their eggs in them and the wasp larvae eat the cockroach eggs.
The Evaniidae Family
Ensign Wasps are in the family Evaniidae and get their name because they move their abdomens up and down as if they are signalling with a flag. They are also known as Hatchet Wasps.
Adults are about 1/4 to 3/4 inch long and can be found feeding on the nectar of flowers and on honeydew that aphids have deposited on leaves, as well as hunting for cockroach egg-cases.
Besides living in Tenerife and the Canary Islands, they are also found in the U.S., Canada, and many other parts of the world. They have followed where cockroaches have gone.
The larva of an Ensign Wasp eats all the eggs it finds in an ootheca and then pupates inside the egg-case.
Adult female Ensign Wasps often come into houses searching for oothecae. Unfortunately, many people kill them, thinking they are harmful pests when the truth is just the opposite. So if you see one, don't destroy it. Either leave it alone or put it outside. It may not look like it, but it is an insect that can be helpful!